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Nov. 11,1958 c. c. MINT ER CURRENT REGULATOR TUBE Filed Jan. 28, 195'!LEE ATTORNEY) United States Patent Office CURRENT REGULATOR TUBE ClarkeC. Minter, Washington, D. C. Application January 28, 1957, Serial No.636,841- 11 Claims. (Cl. 201-63 (Granted under Title 35, U. S. Code(1952), sec. 266) The invention described herein may be manufacturedandused by or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

The present invention relates to current regulating devices and moreparticularly to a ballast tube for automatic regulation of current withminimum lag and hysteresis.

Formerly ballast tubes'have been used to maintain a constant current fora changing voltage source in which the range of regulation issatisfactory but there is substantial time lag in attaining currentstabilization for any change in voltage. The tubes of the prior artusually consist of a small iron wire filament mounted in a sealed glasscontaining hydrogen at a suitable low pressure. Ballasting action is notlimited to the above combination, since other tubes have been made by acombination of other metal filaments and other gases, however, theironhydrogen combination is the most used and best results have beenobtained from this combination.

In order to have ballasting action the metallic filament must have ahigh temperature coefficient of resistance that increases withtemperature such that the resistance of the filament increases morerapidly than the temperature as it is heated. When there is an increasein voltage across the filament, the wire filament of the tube is heatedthereby raising the resistance thereof to electrically account for theincrease in voltage, that is, the increase in voltage is converted bythe filament of the ballast tube into resistance rather than beingdivided across the other portions of the circuit, thereby keeping thecurrent constant.

In order for ballasting to occur, temperature and resistance differencesmust exist in the portion of the current heated filament to causehot-spots, these differences are brought about by 1) local differencesin the diameter of the wire and (2) cooling effect of the supportsholding the filament. In the straight filament type ballast tube inwhich local differences occur, diameter differences of the filamentcause ballasting by creation of hot-spots at the nonuniform points. Theballasting action of ditfernt tubes vary since the wire filaments arenot uniformly made and the ballasting action is only for a short rangeof voltage difference. Due to the cooling of the filament by thesupports there is substantial time lag before the current becomes steadyafter a change in voltage.

In the prior art ballast tubes, not only is there a time lag in currentstabilization after a change in voltage but the ballasting is not thesame for a decreasing voltage as it is for an increasing voltage. Whenballasting is not the same in each direction, hysteresis is introducedand affects the operation of the tube.

It is therefore an object of the present invention to provide a ballasttube which reduces the time lag in voltage adjustments in a ballasttube.

Another object is to provide a ballast tube which reduces hysteresis toa minimum so that current regulation 2,860,223 Patented Nov. 11, 1958 isthe same for a decreasing voltage as it is for an increasing voltage.

Yet another object is to provide a ballast tube which will provideballasting action over a wide range of volt age change.

Still another object is to provide a ballasting tube having non-uniformheating in an isolated filament of uniform diameter.

Other and'more specific objects of this invention will become apparentupon a more careful consideration of the following detailed descriptionwhen taken together with the drawings, in which;

Fig. 1 is a cross-sectional view of one embodiment of this inventionillustrating the relative parts; and

Fig. 2 is a cross-sectional view of a modification of Fig. 1.

In accordance to the present invention ballast action is provided bypositioning a filament of substantially perfect uniform diameter made ofa metal having a high temperature coefficient of resistance whichincreases with an increase in temperature within an envelope structurewhich has portions of the wall structure at varying distances from thefilament. The filament is supported by a spring at one end thereof toallow for expansion and contraction of the filament and to provide ameans for maintaining the filament centrally along the axis of theenvelope.

With particular reference to the drawings wherein like referencecharacters represent like parts throughout, there is shown in Fig. 1 onemodification of a ballast tube 10 provided with a glass or metal jacket11 within which is positioned a double conical envelope 12 of glass ormetal wall structure joined at their bases and secured at each end 13and 14 to the inside of the jacket. A material of substantially perfectuniform diameter having a high temperature coefficient of resistancesuch as a tungsten wire filament 15 or any other suitable material ispositioned along the longitudinal axis of the envelope 12 of metal wallstructureand connected at one end to a lead wire 16 and connected at theopposite end to a spring 17 which is connected to a second lead wire 18.The spring serves as a means for maintaining the filament in axialalignment within the tube. The double conical envelope is filled with asuitable gas such as hydrogen at any suitable low pressure.

The ballast tube can be air-cooled or water cooled and for this purposethe double conical envelope 12 is shown surrounded by the jacket 11. Ifdesired, the tube can be constructed without the jacket 11 and in thiscase the envelope 12 Will be closed at the ends thereof and the leadWires 16 and 18 must be insulated therefrom.

In operation of the modification shown in Fig. 1, the tube is'positionedin a circuit having a desired variable voltage source. When a voltagedrop is applied across the filament 15, the filament heats-up due to thecurrent flow and the resistance of the wire changes as the wireheats-up. The double conical envelope 12 having a varying distance fromthe filament will tend to absorb heat more readily from the ends of thefilament than at the midpoint thereof thus causing the filament todevelop a hot-spot at its midpoint. This hot-spot provides theballasting action for the tube and as the current momentarily increasesby increasing the voltage across the filament, the filament gets hotterraising the resistance thereof from the midpoint toward the ends whichstabilizes the current. The varying distance of the envelope from thefilament absorbs heat from the filament according to the distancebetween the filament and the wall surface and therefore causes thefilament to heat more readily from the midpoint towards the ends toprovide a constant current for the circuit over a limited voltage rangeone to U the change in resistance of the filament as the filamentheats-up.

In reference to Fig. 2, there is shown a modification of Fig. l whichhas essentially all the elements of Fig. 1. As shown, the envelope wallstructure 21 is made of glass or metal having end surfaces 22 and 23 ofequal diameter between which is formed wall sections 24, 25, 26, 27 and28. Sections 25 and 27 are cylindrical sections equal in diameter to theend sections whereas sections 24, 26, and 28 are of spherical shape,each having a different radii formed successively with a decreased radiifrom one end of the structure toward the other. Lead wires 16 and 18 areinsulated from the wall surface at 31 and 32 such that the filament ispositioned longitudinally along the axis of envelope 21. The structureof Fig. 2 provides aplurality of hotspots as the voltage drop isincreased across the filament and functions similar to the operation ofFig. l. A hotspot is produced first in the spherical section having thegreatest radius since the wall surface is farthest from the filament. Asthe voltage drop is increased hot-spots will develop successively alongthe filament within the spherical section having the next longest radiiuntil the voltage drop is great enough to develop hot-spots at all ofthe spherical surfaces of different radii. Each hot-spot developedproduces greater filament resistance thereby permitting a ballast actionfor a greater variance of voltage..

The modification as shown in Fig. 2 will provide ballast action over amuch greater range than the modification of Fig. l and can also 'beprovided with an envelope for water-cooling'the envelope as shown in themodification of Fig. 1.

For the purposes of this invention tungsten is desired as the filamentmaterial since tungsten is the strongest of the desired metals and canbe made more easily into a filament of substantially perfect uniformdiameter. However the invention is not limited to filaments of tungstenwire since it is obvious that any desired metal of uniform diameter canbe used. As an example, the tubes can be made with a one mil tungstenwire filament approximately seven inches long secured in an envelopefilled with hydrogen to a pressure of about five millimeters of mercury.

The construction of the above described modifications of differentballast tubes will control the current for a decreasing voltage as wellas for an increasing voltage. Due to the construction of the tube,gradual absorption or release of heat by the wall structure causes anincrease or decrease in the resistance of the filament and controls thecurrent across the filament such that there is very little time lag instabilizing the current across the devices in the circuit in which theballast tube is connected.

Obviously many modifications and variations of the present invention arepossible in the light of the above teaching. It is therefore to beunderstood, that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

l. A current regulating tube comprising an elongated envelope containinghydrogen gas, a pair of support leads extending from said envelope, astraight elongated resistance wire filament having a uniform diameterand made of material having a high temperature coefiicient of resistancethat increases with temperature positioned longitudinally along the axisof said envelope, said filament being connected between said supportleads, the surface of said envelope directly opposite said filamenthaving portions of the surface thereof at greater distances from saidfilament than the distance between the ends of said envelope and saidsupport leads, and means for maintaining said filament in axialalignment within said envelope.

2. A current regulating tube comprising an elongated envelope containinghydrogen gas, a pair of support leads extending from said envelope, astraight elongated resistance wire filament having a uniform diameterand made of material having a high temperature coefiicient of resistancethat increases with temperature positioned longitudinally along the axisof said envelope, said filament being connected to and between saidsupport leads, spring means for maintaining said filament in axialalignment within said envelope, and, the surface of said elongatedenvelope directly opposite said filament having portions of the surfacethereof at greater radii from said filament than the distance betweenthe ends of said envelope and said support leads.

3. A current regulating tube comprising an elongated envelope containinghydrogen, a pair of lead supports extending from the ends of saidenvelope along the axis thereof, a straight elongated resistance wirefilament of material having'a high temperature coefficient ofresistancethat increases with temperature and of uniform diameterpositioned longitudinally along the axis of said envelope, said filamentbeing connected to and between said lead supports, spring meansconnected to and between one end of said filament and one of saidsupports for maintaining said filament in axial alignment within saidenvelope, the surface of said elongated envelope directly opposite saidfilament being constructed with portions thereof at different radii fromsaid filament than the distance between the ends of said envelope andsaid support leads.

4. A current regulating tube comprising an elongated double conicalenvelope containing hydrogen gas, a pair of lead supports extending fromsaid envelope along the axis thereof, a straight elongated resistancewire filament of material having a high temperature coefiicient ofresistance that increases with temperature positioned along thelongitudinal axis of said envelope, said filament being connected to andbetween said support leads, means for maintaining said filament in axialalignment within said envelope, said double conical envelope having itsgreatest diameter opposite the midpoint of said filament.

5. A current regulating tube as claimed in claim 4 wherein saidresistance wire filament is of uniform diameter.

6. A current regulating tube' as claimed in claim 5 wherein the envelopeis made of metal.

7. A current regulating tube as claimed in claim 5 wherein said meansfor maintaining said filament in axial alignment within said envelope isa spring of larger diameter wire than said filament and positionedbetween one end of said filament and the end of one of said leadsupports.

8. A current regulating tube comprising an elongated envelope containinghydrogen gas, the surface of said envelope being formed by equallyspaced spherical portions each having different radii and positionedbetween portions extending from the ends of said envelope along the axisthereof, a resistance wire filament of material having a hightemperature coefiicient of resistance that increases with resistancepositioned along the longitudinal axis of said envelope, said filamentbeing connected to and between said lead supports, and means formaintaining said filament in axial alignment within said envelope.

9. A current regulating tube as claimed in claim 8 wherein saidresistance filament wire is of uniform diameter.

10. A current regulating tube as claimed in claim 8 wherein the radii ofeach successive spherical portion is less than the preceding sphericalportion.

11. A current regulating tube as claimed in claim 8 wherein said meansfor maintaining said filament in axial alignment within said enevelopeis a spring of larger diameter wire than said filament and positionedbetween one end of said filament and the end of one of said leadsupports.

References Cited in the file of this patent UNITED STATES PATENTS 6Ruben Apr. 17, 1934 Gertler Aug. 29, 1939 Heddaeus Dec. 29, 1942 WhitmanJan. 4, 1944 FOREIGN PATENTS Great Britain Oct. 2, 1924

